(a) Insulin hormone is secreted by pancreatic islets. Insulin increases the utilization of glucose in tissues and facilitates the storage of glucose as glycogen in muscles and liver. By these actions insulin lowers the blood sugar level.
(b) It is fact that Hypothalamus and Pituitary function as an integrated coordinated system. In hypothalamus, the hormonesvare synthesized in the neurosecretory cells body and then transported along the axon to its tip where the hormones are stored in droplets.
Hypothalamic neuro-secreting cells secrete several hormones called neurohormones into this blood, These reach the anterior pituitary through the
portal blood and control the secretion of hormones
by the cells of that gland.
For example : Thyrotropin releasing hormone, corticotropin releasing hormone and gonadotropin releasing hormone of hypothalamus stimulates the anterior pituitary to secrete the hormones called thyrotropin, corticotropin and gonadotropins respectively. On the other hand the hormone somatostatin of the hypothalamus inhibits the secretion of growth hormone (GH) from the anterior pituitary.
(c) Sex hormones are secreted near the age of puberty or sexual maturity. Testosterone stimulates the development of the external male sex characters such as beards, moustaches, and low pitch male voice in man. Thus, testosterone promotes the growth of many body tissues including bones and muscles. Androgens are such substances which stimulate the development of male sex characters.
(d) Both adrenal medulla and sympathetic nervous
system function as a closely integral system. In man much more adrenaline is secreted than the non-adrenaline. Secretion of these hormones is stimulated when nerve impulses reach the adrenal medulla through sympathetic nerve fibres. Both sympathetic nerves and adrenal medulla are stimulated in physical stress like fall in blood pressure; blood sugar; pain, cold or injury. Both are also stimulated in emotional stress such as anger, fear and grief. All these indicate that the adrenal medulla and the sympathetic nervous system function as closely intergrated system.